Electronic locks are a popular feature of modern safes and strong boxes for several reasons. First, they enable the use of advanced authentication methods including PIN codes, biometric sensors such as fingerprint, palm, or retina scanning, programmed time of day unlocking, or some combination of the above. Second, the use of an electronic lock facilitates the creation of electronic records of opening the lock. Third, unlock codes can be added or modified without the expense of recoding a lock cylinder or cutting new keys as required with mechanical key locks. Fourth, electronic locks can be monitored or actuated remotely if a networking connection is provided.
For their many desirable features, some electronic locks have some drawbacks. Locks designed for safes are most frequently installed inside the bolt work within the safe door as taught, for example, by Maniaci U.S. Pat. No. 6,098,433 and Bremer U.S. Pat. No. 2,171,263. Such placement often leads to having a power source and a controller within the door or wiring a harness over to the door across a moving door hinge boundary.
Gartner U.S. Pat. No. 3,758,142 offers a lock configuration where the electronic locking element is located on the wall side of a safe which serves as an example of how wiring can be avoided across a door hinge boundary. Gartner further addresses another drawback of many electronic safe locks in that they lack assurance that they have effectively locked the safe door in place. Gartner teaches that a lock may include indicating means such as a switch and a light for indicating that the cross bolt is in the locked position to detect false locking. The disclosed mechanical switch arrangement requires a generous volume of working space behind the door sill area of the safe and relies on special features within the cross bolt mechanism to actuate the switch plunger. In Gartner's described configuration, both the cross bolt and the switch plunger may be subjected to physical wear over time resulting in a loss of affirmative lock feedback. Additionally, in Gartner's arrangement, the system has limited ability to automatically manage false latching conditions as the user is required to manually insert a key to force the solenoid to re-energize to once again retract the cross bolt.
It is known in the industry that the driving action of a bolt can be used to trigger a locking mechanism mechanically as exemplified by Gartner. To do so, spring loaded latching mechanisms such as the lever arm taught by Gartner or the spring leaf taught by Dobbins U.S. Patent Application Publication No. 2016/0110939, assigned to the assignee of the present application and incorporated by reference herein in its entirety, are actuated by the bolt to release a plunger mechanism that grabs the bolt in a locked state. These types of mechanical actuation systems may require careful attention to mechanical tolerances of the bolt which is mounted to a sliding or swinging door, with respect to a fixed wall. Typically, these types of tolerances are difficult to control and result in requiring generous over-travel of the bolt or sizeable actuation levers that consume large volumes of space internal to the product.
Electronic bolt position sensing at the wall of the safe advantageously serves as a way of detecting when the door itself is in the fully closed and lockable position. One traditional approach to monitoring whether a door is open or closed is by using a door switch such as a mechanical plunger style switch or a magnetic switch such as a reed switch. A controller is configured to sense when the face or edge of the door contacts or nearly contacts the switching element to indicate the door is closed. One difficulty with such systems is that there is a window of uncertainty as to whether the door is actually closed. In the case of a magnetic switch, both the door mounted magnetic field strength and the reed switch sensitivity levels may not be well controlled. The door switch may register that the door is closed even when it is partially open such that the sensor and magnet are close enough to trigger the switch. In the case of a mechanical door switch, mechanical bracketry and the switch plungers themselves are subject to being bent or otherwise deformed over repeated use that can result in malfunctions. An added drawback to the above described door sensing methods is that they are subject to attach by using a piece of tape across the door switch plunger or a magnet near the reed switch.